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6 CLOUD SEEDING of cloud systems to be treated. It is essential that any prospective cloud seeding project be carefully designed, making full use of the historic meteorological data base and perhaps new data where appropriate infor- mation is not available. All projects require monitoring, not only of generator performance, but also of regional and local weather. Within the U.S. at least, National Weather Service station network data (surface and satellite data and the soon-to-be operational WSR-88D Doppler radar coverage) help to assess but cannot observe all pertinent local weather. Project observations are still necessary for operational decision making and evaluation. Depend- ing on the nature of the project weather, key required sensors may in- clude precipitation gauges, wind sensors, upwind rawinsondes, and a weather radar. Evaluation of operational program results often relies on statistical evaluations because the cost of direct monitoring technologies is high. While there are many pitfalls in this approach, comparisons of precipita- tion observed in nontreated cases can yield some useful guidance. Sea- sonal streamflows or snow course data may also be used in evaluation. Some rudimentary radar and airborne cloud physics measurements often contribute to evaluations. Research projects have largely moved away from purely statistical evaluations and toward physical evaluation derived from direct observa- tions of the seeding material delivery to clouds, the resulting physical chain of events in clouds, the precipitation fallout, and the chemistry of seeded and unseeded precipitation that has reached the ground. The vastly improved numerical models that simulate cloud processes in con- siderable detail, and the many new remote and in situ atmospheric and cloud sensing technologies (e.g., sensor for continuously profiling the wind and temperature) are being applied in the research mode, are gradually moving into operations, and should be reviewed by the would- be cloud seeder and used where affordable for both real-time guidance and post-project evaluation. 1.6 HOW TO INITIATE A CLOUD SEEDING PROJECT In the past, engineers have become involved in the decision-making process leading to implementation of cloud seeding projects, and un- doubtedly this will become more common in the future. The last part of this Manual, Section 6-How to Implement a Cloud Seeding Program, leads the reader through the steps from feasibility to the design study and evaluation plan. The elements of program control and management are also examined. Initial steps toward implementing a seeding program include consid- eration of the need for augmented precipitation, how it would be used, and alternative approaches to satisfying the need. Basic inputs at this